That is the great paradox of Christ. For him to die, he must be man, but for that death to pay for the sins of Mankind, he must also be God. My father describes it thus: that Jesus set aside his divinity and submitted himself to the will of God. It’s like when Peter cut off the ear of the servant of the High Priest and Jesus rebuked him, telling him that if he wanted he could call down legions of angles to save him if he wanted. I think that is the power of the story of Christ, that he forsake his power to dwell on Earth as a man and undergo the punishment of God for the sins of humanity while under the veil of darkness.